I’m glad you love them. With a synthetic topper that’s not heat-friendly, the “beachy wave” look usually has to be created with setting techniques, not heat. A few things that can work:

Try a wet set: lightly mist the hair with water, apply a tiny bit of wig mousse or setting foam, then wrap it on flexi rods or foam rollers (bigger rods for soft waves). Let it dry fully overnight, then gently separate with your fingers.

Braid method: do 2 to 4 loose braids on slightly damp hair (again with a little mousse), let it dry completely, then shake it out.

Finish for softness: once it’s set, use a small amount of silicone wig spray to take away stiffness and make it look more “airy.”

One important note: some synthetic fibers will only “hold” a wave if they’re heat-friendly, and steam or hot water can ruin certain toppers, so I’d check the brand’s care guide first or test a tiny hidden piece.